Blister packages comprise a package part in the form of a hot formed plastic sheet usually of the transparent type. The plastic sheet is provided with at least one deep embossed portion, which forms a container for the article to be packed. Thus, the plastic sheet forms the laterals and the top portions of the container, but the package requiring an additional closing sheet on the side of the embossed cavity left open. It is therefore a very common feature that a piece of cardboard is placed against the plastic sheet to be secured to the same. In certain cases a container stretching in opposite directions from the plastic sheet is desired, and then two deepembossed plastic sheets can be laid together, their plane, not embossed portions being fitted to each other. There are also packages in which the plastic sheet has been folded, so that two portions are formed, which can be fitted to each other.
In order to hold together the two parts or portions thus required for the sealing of the package, a great number of different means have been used. Staples or similar and a seal made by means of a glueing or welding operation are quite common. It has also been suggested that tube shaped projections might be shaped in the plastic sheet by means of a hot forming operation, which projections might be riveted to a retaining rivet head. More particularly the invention relates to this type of securing means.